The present invention relates to variable valve mechanisms.
Variable valve actuating mechanisms enable the variation of the timing, lift and duration (i.e., the valve lift profile) of associated valves, such as, for example, the valves of an internal combustion engine. Two examples of variable valve actuating mechanisms are detailed in commonly-assigned U.S. Pat. Nos. 5,937,809 and 6,019,076, the disclosure of which are incorporated herein by reference.
As related to internal combustion engines, conventional variable valve mechanisms are associated with a cam or input shaft of the engine. More particularly, a conventional variable valve mechanism typically includes a roller which engages an input cam of the input shaft or the engine camshaft. One or more link or rocker arms carry and link the roller to an output cam. Rotation of the input cam displaces the roller to create oscillatory movement of the components coupled thereto, such as link or rocker arms, relative to the central axis of the input shaft or camshaft. The oscillatory movement of the components that are coupled to the roller, in turn, directly or indirectly oscillate an output cam and thereby actuate one or more valves of the engine.
A biasing means, such as one or more return springs, is generally required in order to maintain the roller in contact with the input cam thereby reducing any mechanical lash. The use of return springs, however, negatively impacts the durability and limits the operating range of conventional variable valve mechanisms, thereby limiting the range of engine operation speeds over which the variable valve mechanism can be efficiently utilized. In addition to return springs, conventional variable valve mechanisms typically include numerous other component parts, such as link arms, joints, pins and frames, and are thus relatively complex mechanically. The numerous component parts increase the cost of the mechanism and make the mechanism more difficult to assemble and to manufacture.
Many of these numerous component parts are directly or indirectly coupled to the roller, and are therefore caused to pivot relative to the central axis of the input shaft as the input cam displaces the roller. Each of these components parts increase the mass of the structure which undergoes pivotal movement, and thereby further limits the range of engine operation speeds over which the variable valve mechanism can be used. The joints and pins that interconnect the component parts of a conventional variable valve mechanism are subject to interfacial frictional forces that negatively impact durability and efficiency of the mechanism.
As stated above, conventional VVA mechanisms generally include one or more link or rocker arms that carry and/or connect the roller of the mechanism with the output cam of the mechanism. The use of links and/or rockers increase the size of the VVA mechanism, and thus a larger space is required in order to install the VVA mechanism within the engine. The links and rocker arms are typically coupled together by joints and/or pins, which further increase the number of component parts and make the VVA mechanism relatively complex from a mechanical standpoint. Furthermore, the joints and pins are subject to interfacial frictional forces that negatively impact durability and efficiency. Moreover, the link adds to the oscillatory mass of the VVA mechanism, and thereby limits the effective engine operating range within which the VVA mechanism can be used.
Therefore, what is needed in the art is a variable valve mechanism having fewer component parts.
Furthermore, what is needed in the art is a variable valve mechanism with fewer joints and/or pins, and thus has reduced frictional losses.
Still further, what is needed in the art is a variable valve mechanism that eliminates the use of return springs, and is therefore operable over an increased range of engine operating speeds.
Moreover, what is needed in the art is a variable valve mechanism that has reduced pivoting mass, and is therefore operable over an increased range of engine operating speeds.
The present invention provides a belt-driven variable valve actuating mechanism.
The invention comprises, in one form thereof, a rocker having a central rocker axis that is substantially parallel with and spaced apart from a central axis of a rotary input shaft. A frame member has a first end configured for being pivotally mounted upon the input shaft and a second end pivotally carrying the rocker. A connecting rod has a first end configured for engaging an eccentric of the rotary input shaft and a second end pivotally attached to the rocker. The connecting rod transfers rotation of the input shaft to oscillation of the rocker relative to the rocker central axis. An output cam is configured for being pivotally mounted upon the input shaft. A belt engages the rocker and the output cam, and transfers oscillation of the rocker to oscillation of the output cam.
An advantage of the present invention is that it uses fewer component parts relative to a conventional variable valve mechanism, thereby reducing the cost and complexity of the mechanism.
Another advantage of the present invention is that fewer joints/pins are necessary relative to a conventional variable valve mechanism, thereby reducing frictional losses and increasing durability of the mechanism.
A still further advantage of the present invention is that return springs are not required, thereby further increasing the durability of the mechanism and enabling use of the mechanism over a wider range of engine operating conditions.
An even further advantage of the present invention is that the pivoting mass is substantially reduced, thereby rendering the mechanism operable over a wider range of engine operating speeds.